1. Field of the Invention
This invention relates to a press, such as a shell press for manufacturing can ends for beverage and like cans, and more particularly to a cam actuated ejector mechanism for ejecting formed parts from a press.
2. Description of the Prior Art
The shell press with which the present invention can be used forms shells, which are the ends of beverage or food cans, that are later seamed to can bodies. The shells are formed from wide strips of steel, aluminum, or other suitable material and may be formed in groups of ten, twelve, etc. When formed in such groups, for example ten at a time, two rows of five shells will be formed from the width of material, and the rows will be disposed so that the shells of one row will be staggered in relation to the shells of an adjacent row in order to minimize skeleton material, i.e., the material left after the parts are blanked out.
There are principally two types of ejectors for shells of which the applicant is aware. In the first type, the ejector is mounted on the shell press and includes a plurality of arms that inwardly swing underneath the slide to eject the shell after it has been formed. The arms' forward or extending motion is spring actuated, while their rearward or retracting motion is mechanically actuated. When the shells are positioned for ejection, the kicker arms are mechanically released and accelerated by spring action into the forming area to eject the shells onto tracks that are downwardly inclined to deliver the shells to a conveyor for conveyance to subsequent stations.
There are a number of disadvantages associated with the above ejector which undesirably affect the production of shells. Firstly, since the ejector arms are spring actuated, they quickly accelerate to a high speed before engaging the shells, and, upon striking the shells, often deform some of the shells due to the large force with which they are struck. When this occurs, the shells are unsuitable for seaming with can bodies and must be discarded and replaced. Secondly, because the ejector arms move in an arcing manner into and out of the slide area, the press slide may not be closed to form the next shell until the last ejector arm has cleared its path. Further, because the shells are formed in a staggered manner to minimize the skeleton, certain of the shells are more inwardly disposed in the slide area, thereby necessitating that their ejector arms be longer than adjacent ejector arms. Therefore, it follows that these longer arms will have much longer strokes into and out of the slide area, greater masses, and require more clearance and time to be withdrawn out of the slide area, which slows the production of shells by the press.
Thirdly, and related to the spring actuation of the ejector arms, the forward or extending movement of the ejector arms is purely a function of spring tension and is independent of the speed of the press. Such spring actuation does not permit desirable and efficient synchronous motion of the ejector with the press.
Fourthly, since the ejector arms move independently of the press, they cannot be optimally released until adequate clearance is provided in the forming area. This necessitates the precautionary step of not releasing the ejector arms until sufficient clearance is available, thereby creating undesirable dead time between the release of the ejector arm and ejection of the shell.
Fifthly, all springs experience fatigue after a certain number of cycles resulting in progressively weaker spring forces to accelerate the released ejector arms. At a certain point in time, the springs may not possess sufficient force to properly eject shells, and should the operator tighten the spring to maintain the required spring force, failure of the spring will only be accelerated since it will now no longer be operating within its proper range of deformation.
In the second type of ejector with which the applicant is familiar, a plurality of rods or bars reciprocate within a plane underneath the slide of the press to eject the shells. The rods or bars are so disposed relative to the slide that they eject half of the shells in one direction and the other half in the opposite direction. Like the first ejector mechanism, this second type also utilizes spring force to release the rods or bars, which are then retracted by a mechanical device, for example a cam. Consequently, this latter ejector has undesirable characteristics of the former, for example, deformation of some of the shells due to the large force with which they are struck by the spring actuated rods or bars, forward movement of the rod or bars independent of the speed of the press, and progressive fatigue and eventual failure of the springs.